Multilayer circuit board

ABSTRACT

A multilayer circuit board includes: two or more layers of electrical insulative base members; and two or more layers of conductive patterned layers. At least two of the conductive patterned layers include coil patterns that will be a part of a coil, through holes are provided at predetermined positions of the electrical insulative base members, the positions being sandwiched between the coil patterns, so as to enable communication between respective end portions of the coil patterns, and conductive paste charged in the through holes allows electrical connection to be established between the respective end portions. The coil is formed so as to be wound in a direction perpendicular to a thickness direction of the multilayer circuit board. With this configuration, a multilayer circuit board can be provided, which facilitates increasing the winding number of a coil and has excellent flexibility of circuit design.

FIELD OF THE INVENTION

The present invention relates to a multilayer circuit board including a coil.

BACKGROUND OF THE INVENTION

As conventionally known methods for forming a coil, there is a method of forming a plurality of coil patterns, each of which will be a part of a coil, in a circuit board and then connecting these coil patterns electrically so as to form a coil. For instance, as shown in FIG. 9, JP 2001-77538A suggests that coil patterns 402a to 402d shaped like a letter C are formed on principal surfaces of respective layers 401a to 401c of a build-up multilayer board 400, and the coil patterns 402a to 402d are connected via build-up vias 403a to 403c so as to form a circuit board including a patterned coil with a spiral shape as a whole.

Furthermore, as shown in FIG. 10, JP 2000-223316A suggests a circuit board having a coil structure formed as follows: a plurality of coil patterns 501 and 502 are formed to be aligned on upper and lower surfaces 500a and 500b of a board 500, and end portions 501a and 502a of the respective coil patterns 501 and 502, provided backward (upper right side) of this drawing, are connected electrically with each other via a plurality of conductive portions 503a formed to penetrate the board 500. Similarly, end portions 501b and 502b of the respective coil patterns 501 and 502, provided forward (lower left side) of this drawing, are connected electrically with each other via a plurality of conductive portions 503b formed to penetrate the board 500.

According to these circuit boards, there is no need for separately mounting a coil on the circuit board, thus enhancing the working efficiency during the manufacturing of a circuit.

However, for the patterned coil described in JP 2001-77538A, the coil patterns are provided on principal surfaces of the respective layers of the board. Therefore, in order to increase the winding number of the coil, the number of layers of the board has to be increased. Although the winding number of the coil has to be increased for obtaining a larger inductance, the winding number of the above-mentioned patterned coil is restricted to the number of the layers of the board as described above. Therefore, if an inductance larger than a predetermined threshold value is required, it may be difficult to increase the winding number. Also, when the number of the layers of the board is increased for obtaining a larger inductance, displacement in the lamination may occur. In an extreme case, the connection of build-up vias with coil patterns formed between the layers may become unstable, resulting in electrical discontinuity.

On the other hand, the coil structure described in JP 2000-223316A is wound in the direction perpendicular to the thickness direction of the board, and therefore the winding number of the coil can be increased in this winding direction. However, since the board is a so-called double-sided circuit board including a single layer of an electrical insulative base member and conductive patterned layers formed on both principal surfaces of this electrical insulative base member, there is a possibility of lowering the flexibility of circuit design. For instance, since a single-winding coil only can be provided in the thickness direction of the board, if an inductance larger than a predetermined threshold value is required, it may be difficult to increase the winding number. Further, there is a possibility of the failure to provide members having various functions, which will described later, including a shielding function, a current detection function and the like, separately.

SUMMARY OF THE INVENTION

In order to cope with the above-stated problems, it is an object of the present invention to provide a multilayer circuit board that facilitates increasing the winding number of a coil and has excellent flexibility of circuit design.

The multilayer circuit board of the present invention includes: two or more layers of electrical insulative base members; and two or more layers of conductive patterned layers. Each of the conductive patterned layer is disposed on at least one selected from: an outer surface of one of the electrical insulative base members that is an outermost layer; and an interface between the respective electrical insulative base members. At least two of the conductive patterned layers include coil patterns that will be a part of a coil. Through holes are provided at predetermined positions of the electrical insulative base members, the positions being sandwiched between the coil patterns, so as to enable communication between respective end portions of the coil patterns. Conductive paste charged in the through holes allows electrical connection to be established between the respective end portions, whereby the coil is formed so as to be wound in a direction perpendicular to a thickness direction of the multilayer circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a multilayer circuit board according to Embodiment 1 of the present invention, showing each layer separately, and FIG. 1B is a cross-sectional view of the multilayer circuit board according to Embodiment 1 taken along the line I-I of FIG. 1A.

FIG. 2 is a perspective view of a layer provided with a coil in a multilayer circuit board according to Embodiment 2 of the present invention.

FIG. 3A is a perspective view of a multilayer circuit board according to Embodiment 3 of the present invention, showing each layer separately, and FIG. 3B is a cross-sectional view of the multilayer circuit board according to Embodiment 3 taken along the line II-II of FIG. 3A.

FIG. 4A is a perspective view of a multilayer circuit board according to Embodiment 4 of the present invention, showing each layer separately, and FIG. 4B is a cross-sectional view of the multilayer circuit board according to Embodiment 4 taken along the line III-III of FIG. 4A.

FIG. 5A is a perspective view of a multilayer circuit board according to Embodiment 5 of the present invention, showing each layer separately, and FIG. 5B is a cross-sectional view of the multilayer circuit board according to Embodiment 5 taken along the line IV-IV of FIG. 5A.

FIG. 6A is a perspective view of a multilayer circuit board according to Embodiment 6 of the present invention, showing each layer separately, and FIG. 6B is a cross-sectional view of the multilayer circuit board according to Embodiment 6 taken along the line V-V of FIG. 6A.

FIG. 7A is a perspective view of a multilayer circuit board according to Embodiment 7 of the present invention, showing each layer separately, and FIG. 7B is a cross-sectional view of the multilayer circuit board according to Embodiment 7 taken along the line VI-VI of FIG. 7A.

FIG. 8 is a perspective view of a multilayer circuit board according to Embodiment 8 of the present invention, showing each layer separately.

FIG. 9 is a perspective view showing a conventional patterned coil.

FIG. 10 is a perspective view showing a conventional coil structure.

DETAILED DESCRIPTION OF THE INVENTION

The multilayer circuit board of the present invention (hereinafter, also simply referred to as a “board”) may include: two or more layers of electrical insulative base members; and two or more layers of conductive patterned layers. Each of the conductive patterned layer may be disposed on at least one selected from: an outer surface of one of the electrical insulative base members that is an outermost layer; and an interface between the respective electrical insulative base members.

As the electrical insulative base members, a member containing: 20 weight % to 70 weight %, inclusive, of an aramid non-woven cloth or a glass non-woven cloth; and 30 weight % to 80 weight %, inclusive, of a thermosetting resin can be used. The thermosetting resin preferably includes at least one selected from the group consisting of an epoxy resin, an aramid epoxy resin, a phenol resin and a cyanate resin. The conductive patterned layers can be formed by a well-known method, for example, which can be obtained by patterning a metal foil such as copper foil by a photolithographic method.

Further, according to the multilayer circuit board of the present invention, at least two of the conductive patterned layers may include coil patterns that will be a part of a coil, through holes may be provided at predetermined positions of the electrical insulative base members, the positions being sandwiched between the coil patterns, so as to enable communication between respective end portions of the coil patterns, and conductive paste charged in the through holes may allow electrical connection to be established between the respective end portions. With this configuration, a conductive portion made of the conductive paste is formed in the through hole, and a coil conductor including this conductive portion and the coil pattern is formed. Then, the coil conductors corresponding to the winding number of the coil in number are connected, whereby a coil is formed so as to be wound in a direction perpendicular to a thickness direction of the board.

In this way, according to the multilayer circuit board of the present invention, a coil is formed so as to be wound in a direction perpendicular to a thickness direction of the multilayer circuit board. Therefore, the winding number of the coil can be increased easily in this winding direction.

Further, since the multilayer circuit board of the present invention includes two or more layers of electrical insulative base members, the flexibility of circuit design can be enhanced. For instance, in the case where no coil patterns are formed on at least one of both principal surfaces of the board, a component such as a capacitor can be mounted directly above the coil. In this case, the direction of the magnetic flux generated from the coil becomes parallel with the principal surfaces, and therefore the component mounted on the principal surface becomes less prone to being affected by the noise due to the change in magnetic flux generated from the coil.

Further, an outer shape of the coil may have a toroidal shape. Such a toroidal outer shape of the coil allows the leakage of the magnetic flux generated from the coil to be decreased, so that actual values of inductance will be approximate to the theoretical value. Thereby, inductances can be obtained with accuracy, which facilitates the design of a circuit.

Further, in the case where the multilayer circuit board of the present invention includes: three or more layers of the electrical insulative base members; and four or more layers of the conductive patterned layers, the winding number of the coil can be increased not only in the direction perpendicular to the thickness direction of the board, but also in the thickness direction of the board. For instance, in the case of using a three-layered electrical insulative base members, a coil can be formed to be double-wound continuously in the thickness direction of the board. In the case of using (2n+1)-layered electrical insulative base members, a coil can be formed to be (n+1)th-wound, at the maximum, continuously in the thickness direction of the board, where n represents a natural number. With this configuration, a coil with a large inductance can be obtained.

Note here that the winding number of the coil provided in the multilayer circuit board of the present invention is not limited in either of the thickness direction of the board and the direction perpendicular to the thickness direction of the board, and the winding number can be set appropriately depending on the intended use. Further, the through holes enabling the communication between the respective end portions of the coil patterns can be formed by a well-known method, for example, by laser processing or the like. Further, the conductive paste charged in the through holes is not limited particularly, and preferably, a conductive paste containing: a powder made of at least one type of metal selected from the group consisting of silver, copper, gold and nickel; and a thermosetting resin such as an epoxy resin is used in order to secure the stable electrical connection.

Further, in the case where the multilayer circuit board of the present invention includes three or more layers of the electrical insulative base members, metal foils further may be disposed on both principal surfaces of the multilayer circuit board so as to sandwich the coil. With this configuration, the magnetic field generated from the coil can be shielded.

Further, the multilayer circuit board of the present invention may be configured so that no conductive patterned layer is formed on at least one of both principal surfaces of the multilayer circuit board. With this configuration, the principal surface with no conductive patterned layers formed thereon is isolated electrically, and therefore the board can be attached directly to a metal enclosure or the like where this principal surface serves as the attachment surface.

Further, in the case where the multilayer circuit board of the present invention includes three or more layers of the conductive patterned layers, at least one of the conductive patterned layers may include a circuit wiring, and at least a part of the circuit wiring may be disposed inside the coil. With this configuration, a function of detecting a current flowing through the circuit wiring can be assigned to the coil.

Further, the multilayer circuit board of the present invention may include a plurality of the coils having different winding numbers, and the plurality of coils may be each disposed within a range enabling interaction of mutual magnetic fields. With this configuration, a voltage conversion function can be assigned to the coil. Moreover, in this configuration, a magnetic member further may be disposed inside the plurality of coils. According to this configuration, a voltage conversion function with excellent transmission efficiency can be assigned to the coil. Note here that the wording “disposed within a range enabling interaction of mutual magnetic fields” represents that, in the case where a multilayer circuit board includes a first coil and a second coil, for example, the second coil is disposed within a range in which the magnetic field generated by the first coil acts and the first coil is disposed within a range in which the magnetic field generated by the second coil acts.

Further, the multilayer circuit board of the present invention may include a plurality of the coils having a uniform winding number, and the plurality of coils may be each disposed within a range enabling interaction of mutual magnetic fields. With this configuration, a noise filter function can be assigned to the coil. The following describes embodiments of the present invention in detail.

EMBODIMENT 1

Firstly, Embodiment 1 of the present invention will be described below, with reference to the drawings as needed. FIG. 1A to be referred to in the following is a perspective view of a multilayer circuit board according to Embodiment 1 of the present invention, showing each layer separately, and FIG. 1B is a cross-sectional view of the multilayer circuit board according to Embodiment 1 taken along the line I-I of FIG. 1A.

As shown in FIGS. 1A and 1B, a multilayer circuit board 1 according to Embodiment 1 of the present invention includes: electrical insulative base members 2 a, 2 b and 2 c; a conductive patterned layer 3 a provided between the electrical insulative base member 2 a and the electrical insulative base member 2 b; a conductive patterned layer 3 b provided between the electrical insulative base member 2 b and the electrical insulative base member 2 c; and conductive patterned layers 4 a and 4 b respectively provided on outer surfaces 21 a and 21 c of the electrical insulative base members 2 a and 2 c (i.e., both principal surfaces of the multilayer circuit board 1). Thicknesses of the respective layers are for example as follows: the electrical insulative base members 2 a to 2 c are about 8 to 500 μm in thickness and the conductive patterned layers 3 a, 3 b, 4 a and 4 b are in the range of about 3 to 50 μm in thickness.

As shown in FIG. 1A, the conductive patterned layer 3 a includes: a plurality of coil patterns 10 that are formed parallel with each other to have a uniform length; a land 11; and a conductor 12. The conductive patterned layer 3 b includes: a plurality of coil patterns 13 that are formed parallel with each other to have a uniform length, coil end portions 14 a and 14 b; lands 15 a and 15 b; and a conductor 16. The coil patterns 10 and 13 each have a width ranging from about 10 to 10,000 μm, for example. Pitches of the coil patterns 10 and 13 range from about 30 to 3,000 μm, for example.

Further, the coil patterns 10 and 13 respectively include a plurality coil pattern end portions 10 a and 13 a provided backward of FIG. 1A and a plurality of coil pattern end portions 10 b and 13 b provided forward of FIG. 1A. Then, the coil end portion 14 a is provided in a row arrangement with the coil pattern end portions 13 a and the coil end portion 14 b is provided in a row arrangement with the coil pattern end portions 13 b. Herein, the minimum diameter of the respective end portions preferably is 20 μm or more so as to secure the stable electrical connection. Further, the coil end portion 14 a and the coil pattern end portions 13 a are disposed at positions right in the back of the corresponding coil pattern end portions 10 a, respectively. Similarly, the coil end portion 14 b and the coil pattern end portions 13 b are disposed at positions right in the back of the corresponding coil pattern end portion 10 b, respectively. It should be noted that the coil pattern end portions 10 a, 10 b, 13 a and 13 b correspond to “respective end portions of the coil patterns” recited in claims.

The electrical insulative base member 2 b is provided with a plurality of through holes 17 a along the thickness direction of the electrical insulative base member 2 b, where the through holes 17 a enable the communication of the coil end portion 14 a and the coil pattern end portions 13 a with the coil pattern end portions 10 a. Similarly, the electrical insulative base member 2 b is provided with a plurality of through holes 17 b along the thickness direction of the electrical insulative base member 2 b, where the through holes 17 b enable the communication of the coil end portion 14 b and the coil pattern end portions 13 b with the coil pattern end portions 10 b. The minimum diameter of the through holes 17 a and 17 b preferably is 10 μm or more so as to secure the stable electrical connection.

Then, the through holes 17 a and 17 b are filled with conductive paste, whereby conductive portions 18 a and 18 b are formed, and the respective end portions are connected electrically with each other as shown in FIG. 1B. With this configuration, a coil 19 is formed so as to be wound in the direction perpendicular to the thickness direction of the multilayer circuit board 1. Since this coil 19 is wound in the direction perpendicular to the thickness direction of the multilayer circuit board 1, the direction of the magnetic flux generated from the coil 19 becomes parallel with the outer surfaces 21 a and 21 c of the electrical insulative base members 2 a and 2 c. As a result, as shown in FIGS. 1A and 1B, components 5 a, 5 b and 5 c (indicated by alternate long and short dash lines in the drawings) packaged on the conductive patterned layers 4 a and 4 b become less prone to being affected by the noise due to the change in magnetic flux generated from the coil 19. In addition, according to the present embodiment, the coil 19 is formed within the multilayer circuit board 1, and therefore the components 5 a, 5 b and 5 c become even less prone to being affected by the noise compared with the above-stated conventional double-sided circuit board equipped with a coil configuration (See FIG. 10).

The electrical insulative base member 2 b further is provided with a through hole 17 c that allows the communication of the land 11 with the land 15 a. Similarly to the through holes 17 a and 17 b, this through hole 17 c also is filled with conductive paste, whereby a conductive portion 18 c is formed. With this configuration, the land 11 and the land 15 a are connected electrically with each other.

The electrical insulative base member 2 a is provided with a through hole 30 a and a through hole 30 b, where the through hole 30 a allows the communication of the conductive patterned layer 4 a with the conductor 12 and the through hole 30 b allows the communication of the conductive patterned layer 4 a with the land 11. Then, the respective through holes 30 a and 30 b are filled with conductive paste, whereby conductive portions 31 a and 31 b are formed. With this configuration, the conductive patterned layer 4 a and the conductor 12 or the land 11 are connected electrically with each other.

The electrical insulative base member 2 c is provided with a through hole 32 a, a through hole 32 b and a through hole 32 c, where the through holes 32 a allows the communication of an outermost layer end portion 40 a provided at the conductive patterned layer 4 b with the coil end portion 14 a, the through hole 32 b allows the communication of an outermost layer end portion 40 b provided at the conductive patterned layer 4 b with the coil end portion 14 b, and the through hole 32 c allows the communication of an outermost layer end portion 41 provided at the conductive patterned layer 4 b with the land 15 b. Then, the respective through holes 32 a, 32 b and 32 c are filled with conductive paste, whereby conductive portions 33 a, 33 b and 33 c are formed. With this configuration, the outermost layer end portions 40 a, 40 b and 41 are connected electrically with the coil end portion 14 a, the coil end portion 14 b and the land 15 b, respectively.

Note here that, in the present embodiment, although the conductive patterned layers 4 a and 4 b are provided on the outer surfaces 21 a and 21 c of the electrical insulative base members 2 a and 2 c, the multilayer circuit board of the present invention is not limited to this. For instance, the outer surface 21 a of the electrical insulative base member 2 a may be an electrical insulative surface, instead of the provision of the conductive patterned layer 4 a. With this configuration, the multilayer circuit board 1 can be attached directly to a metal enclosure or the like, where such an outer surface 21 a of the electrical insulative base member 2 a serves as the attachment surface.

The following describes an exemplary manufacturing method of the multilayer circuit board 1 according to Embodiment 1 of the present invention. Firstly, protective films made of polyethylene terephthalate or the like are laminated on upper and lower surfaces of the electrical insulative base member 2 b containing a thermosetting resin, and the through holes 17 a, 17 b and 17 c are formed at predetermined positions by means of laser processing or the like. Next, these through holes 17 a, 17 b and 17 c are filled with conductive paste by means of printing or the like, and then the protective films are peeled off. Thereby, prepregs can be obtained, in which the conductive paste protrudes by the thickness of the protective films. Subsequently, copper foils are disposed on upper and lower surfaces of these prepregs, and hot pressing is applied thereto with 0.5 to 100 MPa of pressure and at 150 to 260° C. of temperature for 5 minutes to 3 hours, for example, whereby the electrical insulative base member 2 b is bonded to the copper foils and the conductive paste charged in the through holes 17 a, 17 b and 17 c allows electrical continuity to be established between the copper foils on the upper and the lower surfaces. Thereafter, the copper foils on the upper and the lower surfaces are patterned as shown in FIG. 1A, whereby a double-sided circuit board 1 a (See FIGS. 1A and 1B) can be obtained. Furthermore, prepregs filled with conductive paste are disposed in a manner similar to the above on upper and lower surfaces of this double-sided circuit board 1 a with the double-sided circuit board 1 a used as a core member, and copper foils are disposed on the outsides thereof, followed by hot pressing and patterning, whereby the multilayer circuit board 1 can be obtained.

EMBODIMENT 2

The following describes Embodiment 2 of the present invention, with reference to the drawings as needed. FIG. 2 to be referred to in the following is a perspective view of a layer provided with a coil in a multilayer circuit board according to Embodiment 2 of the present invention. Since Embodiment 2 is different from Embodiment 1 only in the outside shape of the coil, the following describes such a difference only.

As shown in FIG. 2, a multilayer circuit board 50 according to Embodiment 2 of the present invention includes: conductive patterned layers 52 a and 52 b provided on upper and lower surfaces of an electrical insulative base member 51 b (corresponding to the electrical insulative base member 2 b of Embodiment 1), respectively. Although not illustrated, an electrical insulative base member is provided on the outside of each of the conductive patterned layers 52 a and 52 b, and a conductive patterned layer further is provided on the outside of each electrical insulative base member.

At the conductive patterned layer 52 a, a plurality of coil patterns 53 having a uniform length are disposed in a toroidal shape. At the conductive patterned layer 52 b, a plurality of coil patterns 54 having a uniform length are disposed in a toroidal shape, and coil end portions 55 a and 55 b further are provided. The coil patterns 53 and 54 respectively have a plurality of coil pattern end portions 53 a and 54 a on their inner radius sides and a plurality of coil pattern end portions 53 b and 54 b on their outer radius sides. The coil end portion 55 a is disposed on the inner radius side of the coil patterns 54, and the coil end portion 55 b is disposed on the outer radius side of the coil patterns 54. Further, the coil end portion 55 a and the coil pattern end portions 54 a are disposed at positions right in the back of the respective corresponding coil pattern end portions 53 a, and similarly the coil end portion 55 b and the coil pattern end portions 54 b are disposed at positions right in the back of the respective corresponding coil pattern end portions 53 b.

Further, a plurality of conductive portions 57 are formed in a manner similar to Embodiment 1, that is, the plurality of conductive portions 57 penetrate the electrical insulative base member 51 b and enable the communication between the above-mentioned respective end portions (also in embodiments described later, all of their conductive portions are formed in a manner similar to Embodiment 1), so that the conductive portions 57 enable the electrical connection between the above-stated respective end portions. With this configuration, a coil 58 is formed within the multilayer circuit board 50, the coil being wound in the direction perpendicular to the thickness direction of the electrical insulative base member 51 b. Herein, the outer shape of this coil 58 is formed in a toroidal shape. Such a toroidal outer shape of the coil 58 allows the leakage of the magnetic flux generated from the coil 58 to be decreased, so that actual values of inductance will be approximate to the theoretical value. Thereby, inductances can be obtained with accuracy, which facilitates the design of a circuit.

EMBODIMENT 3

The following describes Embodiment 3 of the present invention, with reference to the drawings as needed. FIG. 3A to be referred to in the following is a perspective view of a multilayer circuit board according to Embodiment 3 of the present invention, showing each layer separately, and FIG. 3B is a cross-sectional view of the multilayer circuit board according to Embodiment 3 taken along the line II-II of FIG. 3A.

As shown in FIGS. 3A and 3B, a multilayer circuit board 100 according to Embodiment 3 includes: electrical insulative base members 101 a to 101 c; conductive patterned layers 102 a and 102 b provided between the respective electrical insulative base members 101 a to 101 c; and conductive patterned layers 103 a and 103 b respectively provided on outer surfaces of 1011 a and 101 c of the electrical insulative base members 101 a and 101 c. The multilayer circuit board 100 further includes a first coil 104 a formed inside and a second coil 104 b formed around this first coil 104 a. Both of the first coil 104 a and the second coil 104 b are wound in the direction perpendicular to the thickness direction of the multilayer circuit board 100. Moreover, as described later, the first coil 104 a and the second coil 104 b are connected electrically, so that a coil 104 is formed to be double-wound continuously in the thickness direction of the multilayer circuit board 100.

The first coil 104 a is formed similarly to the coil 19 of Embodiment 1 (See FIGS. 1A and 1B), and coil end portions 105 a and 105 b thereof are provided at the conductive patterned layer 102 b. Then, the coil end portion 105 a is connected electrically with an outermost layer end portion 120 provided at the conductive patterned layer 103 b via a conductive portion 121 formed so as to penetrate the electrical insulative base member 101 c. The coil end portion 105 b is connected electrically with a land 1061 a provided at the conductive patterned layer 102 b via a wiring 107 provided also at the conductive patterned layer 102 b.

The land 1061 a is connected electrically with a land 1091 a provided at the conductive patterned layer 102 a via a conductive portion 108 formed so as to penetrate the electrical insulative base member 101 b. Further, the land 1091 a is connected electrically with a coil pattern end portion 1111 a of a coil pattern 111 provided at the conductive patterned layer 103 a via a conductive portion 110 formed so as to penetrate the electrical insulative base member 101 a. Further, the land 1061 a is connected electrically with a coil end portion 113 a provided at the conductive patterned layer 103 b via a conductive portion 112 formed so as to penetrate the electrical insulative base member 101 c. With this configuration, the coil end portion 113 a, the land 1061 a, the land 1091 a and the coil pattern end portion 1111 a are connected electrically.

Similarly, a coil pattern end portion 1111 b located on the opposite side of the coil pattern end portion 1111 a is connected electrically with a land 1091 b located right in the back of the coil pattern end portion 1111 b, the land 1091 b is connected electrically with a land 1061 b located right in the back of the land 1091 b, and the land 1061 b is connected electrically with a coil pattern end portion 1141 b of a coil pattern 114 located right in the back of the land 1061 b. With this configuration, the coil pattern end portion 1111 b, the land 1091 b, the land 1061 b and the coil pattern end portion 1141 b are connected electrically.

Similarly to the above, the portion from the coil end portion 113 a to a coil end portion 113 b provided at the conductive patterned layer 103 b is connected electrically, so that the second coil 104 b is formed around the first coil 104 a. In this way, the coil 104 is formed so as to be double-wound continuously in the thickness direction of the multilayer circuit board 100. Thereby, the coil 104 with a large inductance can be obtained.

EMBODIMENT 4

The following describes Embodiment 4 of the present invention, with reference to the drawings as needed. FIG. 4A to be referred to in the following is a perspective view of a multilayer circuit board according to Embodiment 4 of the present invention, showing each layer separately, and FIG. 4B is a cross-sectional view of the multilayer circuit board according to Embodiment 4 taken along the line III-III of FIG. 4A.

A multilayer circuit board 150 according to Embodiment 4 of the present invention is configured so that the conductive patterned layer 4 a of the above-stated configuration of Embodiment 1 (See FIG. 1A) is not provided but metal foils 151 a and 151 b respectively are provided on the outer surfaces 21 a and 21 c of the electrical insulative base members 2 a and 2 c. In the following description, the same reference numerals are assigned to the same configurations as those of Embodiment 1 and their explanations are omitted.

As shown in FIGS. 4A and 4B, on the outer surface 21 a of the electrical insulative base member 2 a, the metal foil 151 a is provided by hot pressing or the like so as to cover the substantially entire surface of the plurality of coil patterns 10 formed at the conductive patterned layer 3 a. Further, on the external surface 21 c of the electrical insulative base member 2 c, the metal foil 151 b is provided by hot pressing or the like so as to cover the substantially entire surface of the plurality of coil patterns 13 formed at the conductive patterned layer 3 b, where the metal foil 151 b has such a size as to avoid a short between outermost layer end portions 40 a and 40 b. In this way, since the metal foils 151 a and 151 b are disposed so as to sandwich the coil 19 therebetween, the magnetic field generated from the coil 19 can be shielded. Herein, as the metal foils 151 a and 151 b, copper foil, aluminum foil and the like having a thickness of about 5 to 100 μm can be used, for example.

EMBODIMENT 5

The following describes Embodiment 5 of the present invention, with reference to the drawings as needed. FIG. 5A to be referred to in the following is a perspective view of a multilayer circuit board according to Embodiment 5 of the present invention, showing each layer separately, and FIG. 5B is a cross-sectional view of the multilayer circuit board according to Embodiment 5 taken along the line IV-IV of FIG. 5A.

As shown in FIGS. 5A and 5B, a multilayer circuit board 200 according to Embodiment 5 includes: electrical insulative base members 201 a to 201 e; conductive patterned layers 202 a to 202 d provided between the respective electrical insulative base members 201 a to 201 e; and a conductive patterned layer 203 provided on an outer surface 2011 e of the electrical insulative base member 201 e. In this multilayer circuit board 200, no conductive patterned layer is formed on an outer surface 2011 a of the electrical insulative base member 201 a. With this configuration, the outer surface 2011 a of the electrical insulative base member 201 a is isolated electrically, and therefore the multilayer circuit board 200 can be attached directly to a metal enclosure (not illustrated) or the like where such an outer surface 2011 a serves as the attachment surface.

As shown in FIG. 5A, the conductive patterned layer 202 a includes two coil patterns 204 formed to have a uniform length and parallel with each other. The conductive patterned layer 202 b includes two lands 205 a provided backward of FIG. 5A and two lands 205 b provided forward of FIG. 5A. Similarly, the conductive patterned layer 202 c includes two lands 206 a provided backward of FIG. 5A and two lands 206 b provided forward of FIG. 5A. The conductive patterned layer 202 d includes a coil pattern 207, a coil end portion 208 a and a coil end portion 208 b. The conductive patterned layer 203 is provided with an outermost layer end portion 209 a located right in the back of the coil end portion 208 a and an outermost layer end portion 209 b located right in the back of the coil end portion 208 b.

As shown in FIG. 5B, similarly to the second coil 104 b of Embodiment 3 (See FIGS. 3A and 3B), the portion from the coil end portion 208 a to the coil end portion 208 b is connected electrically, so as to form a coil 210. Further, the coil end portion 208 a and the outermost layer end portion 209 a are connected electrically via a conductive portion 21 a formed so as to penetrate the electrical insulative base member 201 e, and the coil end portion 208 b and the outermost layer end portion 209 b are connected electrically via a conductive portion 211 b also formed so as to penetrate the electrical insulative base member 201 e.

Further, as shown in FIG. 5A, at the conductive patterned layer 202 b, a circuit wiring 212 is formed so as to run between the lands 205 a and 205 b. That is, a portion of this circuit wiring 212 is disposed inside the coil 210. In this way, the multilayer circuit board 200 is configured so as to include a current detection circuit 213 (i.e., the coil 210) that detects a current flowing through the circuit wiring 212.

The following describes the operation of the current detection circuit 213. When a current flows through the circuit wiring 212, an electromotive force is generated at the coil 210 by electromagnetic induction. This electromotive force is measured between the outermost layer end portions 209 a and 209 b, and a current value flowing through the circuit wiring 212 can be determined in accordance with a predetermined conversion formula. Herein, in order to perform the current detection accurately, an operational amplifier (not illustrated) preferably is used for amplifying a voltage obtained between the outermost layer end portions 209 a and 209 b.

Incidentally, although the coil pattern 207 is disposed at the conductive patterned layer 202 d in the present embodiment, the coil pattern 207 may be disposed at the conductive patterned layer 202 c. Further, although the coil 210 is double-wound around the circuit wiring 212, the present invention is not limited to this, and the winding number of the coil can be set appropriately based on the measurement accuracy required for the current detection.

EMBODIMENT 6

The following describes Embodiment 6 of the present invention, with reference to the drawings as needed. FIG. 6A to be referred to in the following is a perspective view of a multilayer circuit board according to Embodiment 6 of the present invention, showing each layer separately, and FIG. 6B is a cross-sectional view of the multilayer circuit board according to Embodiment 6 taken along the line V-V of FIG. 6A.

As shown in FIGS. 6A and 6B, a multilayer circuit board 250 according to Embodiment 6 includes: electrical insulative base members 251 a to 251 e; conductive patterned layers 252 a to 252 d provided between the respective electrical insulative base members 251 a to 251 e; and a conductive patterned layer 253 provided on an outer surface 2511 e of the electrical insulative base member 251 e. Further, inside the multilayer circuit board 250, a first coil 254 a and a second coil 254 b are provided, where the first coil 254 a and the second coil 254 b are disposed within a range enabling the interaction of mutual magnetic fields. Then, the first coil 254 a is double-wound in the direction perpendicular to the thickness direction of the multilayer circuit board 250, and the second coil 254 b is quadruple-wound in the direction perpendicular to the thickness direction of the multilayer circuit board 250. In this way, the multilayer circuit board 250 is configured so as to include a transformer 254 having a voltage conversion function. Herein, the connection between the respective end portions provided in each coil is similar to the above-stated Embodiment 5.

Further, inside the electrical insulative base member 251 c, a groove portion 255 is provided along a center axis common to the first coil 254 a and the second coil 254 b, and a magnetic member 256 is disposed within this groove portion 255. That is, the first coil 254 a and the second coil 254 b are disposed so as to surround the magnetic member 256 and within a range enabling the interaction of mutual magnetic fields. Thereby, the transformer 254 can be provided to have a high transmission efficiency for voltage conversion. Herein, as a material of the magnetic member 256, a thin plate made of iron-based materials such as ferrite, one made by solidifying iron-based powder and the like are preferable.

As for the voltage conversion function, in the case where the first coil 254 a is double-wound and the second coil 254 b is quadruple-wound as in the present embodiment, though depending on the distance between the first coil 254 a and the second coil 254 b, a voltage supply of 2 V from the first coil 254 a side will provide the output of about 3.5 V from the second coil 254 b (reference value).

Although the present embodiment exemplifies the case where the first coil 254 a is double-wound and the second coil 254 b is quadruple-wound, the present invention is not limited to this. The winding number can be set appropriately based on the required output for the convention. Further, although in the present embodiment, the magnetic member 256 is provided along the central axis common to the first coil 254 and the second coil 254 b, the present invention is not limited to this. A transformer can be formed with a plurality of coils having different winding numbers only and without the use of the magnetic member.

EMBODIMENT 7

The following describes Embodiment 7 of the present invention, with reference to the drawings as needed. FIG. 7A to be referred to in the following is a perspective view of a multilayer circuit board according to Embodiment 7 of the present invention, showing each layer separately, and FIG. 7B is a cross-sectional view of the multilayer circuit board according to Embodiment 7 taken along the line VI-VI of FIG. 7A.

As shown in FIGS. 7A and 7B, a multilayer circuit board 300 according to Embodiment 7 includes: electrical insulative base members 301 a to 301 e; conductive patterned layers 302 a to 302 d provided between the respective electrical insulative base members 301 a to 301 e; and a conductive patterned layer 303 provided on an outer surface 3011 e of the electrical insulative base member 301 e.

As shown in FIG. 7A, at the conductive patterned layer 302 a, a plurality of coil patterns 304 having a uniform length are disposed in a toroidal shape. At the conductive patterned layer 302 d, a plurality of coil patterns 305 having a uniform length are disposed in a toroidal shape, and coil end portions 306 a and 306 b further are provided. The coil patterns 304 and 305 respectively have a plurality of coil pattern end portions 304 a and 305 a on their inner radius sides and a plurality of coil pattern end portions 304 b and 305 b on their outer radius sides. The coil end portion 306 a is disposed on the inner radius side of the coil patterns 305, and the coil end portion 306 b is disposed on the outer radius side of the coil patterns 305. Further, the coil end portion 306 a and the coil pattern end portions 305 a are disposed at positions right in the back of the respective corresponding coil pattern end portions 304 a, and similarly the coil end portion 306 b and the coil pattern end portions 305 b are disposed at positions right in the back of the respective corresponding coil pattern end portions 304 b. Further, at the conductive patterned layer 303, outermost layer end portions 309 a and 309 b are provided, which respectively are disposed at positions right in the back of the coil end portions 306 a and 306 b.

As shown in FIG. 7B, the respective end portions are connected electrically via a plurality of lands 310 provided at the conductive patterned layers 302 b and 302 c and via a plurality of conductive portions 307 formed so as to penetrate each of the electrical insulative base members 301 b to 301 e. Thereby, a coil 311 is formed inside the multilayer circuit board 300, the coil 311 being wound in the direction perpendicular to the thickness direction of the multilayer circuit board 300. Then, the outer shape of this coil 311 is formed in a toroidal shape. Further, inside the electrical insulative base member 301 c, a toroidal-shaped groove portion 312 is provided along the inner side of the coil 311, and a toroidal-shaped magnetic member 313 is disposed within this groove portion 312. In this way, the outer shape of the coil 311 is formed in a toroidal shape and the magnetic member 313 is disposed along the inner side of the coil 311, whereby the magnetic flux generated from the coil 311 can concentrate on the inner side of the coil 311, thus further reducing the leakage of the magnetic flux. With this configuration, inductances can be obtained with accuracy, and a larger inductance can be obtained.

EMBODIMENT 8

The following describes Embodiment 8 of the present invention, with reference to the drawings as needed. FIG. 8 to be referred to in the following is a perspective view of a multilayer circuit board according to Embodiment 8 of the present invention, showing each layer separately.

A multilayer circuit board 350 according to Embodiment 8 of the present invention is the same as the above-stated multilayer circuit board 250 of Embodiment 6 (See FIG. 6A) except that the winding number of the first coil 254 a is the same as that of the winding number of the second coil 254 b, and the magnetic member 256 is not provided. In the following description, the same reference numerals are assigned to the same configurations as those of Embodiment 6 and their explanations are omitted.

As shown in FIG. 8, in the multilayer circuit board 350, both of the first coil 254 a and the second coil 254 b are triple-wound in the direction perpendicular to the thickness direction of the multilayer circuit board 350. With this configuration, in the case where the multilayer circuit board 350 is connected with an AC power supply (not illustrated), for example, at the moment in time at which the direction of the flowing current is reversed from the first coil 254 a side to the second coil 254 b side (or from the second coil 254 b side to the first coil 254 a side), the directions of the magnetic fields formed by the currents flowing through the first coil 254 a and the second coil 254 b become opposite to the directions of their respective magnetic fields, and therefore noise due to the change in the magnetic flux generated from each coil can be cancelled out. As a result, each of the first coil 254 a and the second coil 254 b can function as a noise filter.

Note here that, in the present embodiment, a magnetic member is not disposed inside the first coil 254 a and the second coil 254 b. However, a magnetic member may be disposed inside the first coil 254 a and the second coil 254 b as in the above-stated multilayer circuit board 250 of Embodiment 6 (See FIG. 6A). Further, although the present embodiment employs a pair of coils including the first coil 254 a and the second coil 254 b, a circuit may be formed by arranging two or more pairs of coils parallel with each other. In this case, when connecting with an AC power supply, for example, the circuit may be configured so that the phases of the currents flowing through the respective coils forming the coil pairs can be out of phase with each other by 180 degrees. With this configuration, the respective coils can function as a noise filter similarly to the above. Alternatively, when connecting with a DC power supply, the circuit may be configured so that the polarities of the voltages applied to the respective coils forming the coil pairs are different from each other, whereby the coils can function as a noise filter similarly to the above.

The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein. 

1. A multilayer circuit board, comprising: two or more layers of electrical insulative base members; and two or more layers of conductive patterned layers, wherein each of the conductive patterned layer is disposed on at least one selected from: an outer surface of one of the electrical insulative base members that is an outermost layer; and an interface between the respective electrical insulative base members, at least two of the conductive patterned layers comprise coil patterns that will be a part of a coil, through holes are provided at predetermined positions of the electrical insulative base members, the positions being sandwiched between the coil patterns, so as to enable communication between respective end portions of the coil patterns, and conductive paste charged in the through holes allows electrical connection to be established between the respective end portions, whereby the coil is formed so as to be wound in a direction perpendicular to a thickness direction of the multilayer circuit board.
 2. The multilayer circuit board according to claim 1, wherein an outer shape of the coil has a toroidal shape.
 3. The multilayer circuit board according to claim 1, comprising: three or more layers of the electrical insulative base members; and four or more layers of the conductive patterned layers, wherein the coil is at least double-wound continuously in the thickness direction of the multilayer circuit.
 4. The multilayer circuit board according to claim 1, comprising three or more layers of the electrical insulative base members, wherein metal foils further are disposed on both principal surfaces of the multilayer circuit board so as to sandwich the coil.
 5. The multilayer circuit board according to claim 1, wherein no conductive patterned layer is formed on at least one of the principal surfaces of the multilayer circuit board.
 6. The multilayer circuit board according to claim 1, comprising three or more layers of the conductive patterned layers, wherein at least one of the conductive patterned layers comprises a circuit wiring, and at least a part of the circuit wiring is disposed inside the coil.
 7. The multilayer circuit board according to claim 1, comprising a plurality of the coils having different winding numbers, wherein the plurality of coils are each disposed within a range enabling interaction of mutual magnetic fields.
 8. The multilayer circuit board according to claim 7, further comprising a magnetic member disposed inside the plurality of coils.
 9. The multilayer circuit board according to claim 1, comprising a plurality of the coils having a uniform winding number, wherein the plurality of coils are each disposed within a range enabling interaction of mutual magnetic fields. 